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Imagine being able to pinpoint exactly which part of your farm needs more fertiliser to ensure better grass growth without having to take any soil samples -- that's exactly what farmers could do in the future with the use of a new spectral imaging tool.

The $500,000 device was bought last year by Massey University, partly funded through a Primary Growth Partnership programme between Ravensdown and the Ministry for Primary Industries as part of a project to improve how fertiliser is applied to hill country.

Since then the university has been trialling the aerial imaging on eight farms -- five in the North Island and three in the South Island -- and is hopeful the technology will soon be available for use by other farmers, agricultural businesses and even councils.

The seven-year programme is expected to generate $120 million a year in additional export earnings by 2030 and net economic benefits of $734 million between 2020 and 2050.

Ian Yule, professor of precision agriculture at Massey, said buying the device was a "bit of a leap of faith. When we started, I think I was the only one who thought it would work. People thought it sounded too good to be true."

Yule said the model it had bought was not the "Rolls Royce" of spectral imaging machines but it met the requirements. "We did a lot of ground work and knew the spectral range we would need."

The device is the only one of its type in the Asia Pacific region, although others are used in Europe and America on varying applications including the military. It helped that the company which manufacturers them allowed the university to test it first.

The device is about the size of a printer and weighs around 75kg.

Placed in a small aircraft, it can deliver highly detailed images of the land covering 1000 hectares in one hour.

Yule said everything had a spectral signature and the device allowed them to measure different aspects of the soil and plant life. It could also be used on meat to tell if the animal it came from was female or male.

Yule said initially the sensor had to be calibrated and its findings validated through tests undertaken by ground crews. "We have proven the technology works. It can generate new knowledge."

Now it was about working out how to use that information to farm better, he said.

Applying fertiliser through top-dressing is one area where it could make a big difference -- by allowing it to be spread at different rates depending on the requirements of the soil. "Previously you could make really good maps and plans but it would still rely on the pilot manually using a lever."

The new imaging would allow it to be automated, leaving the pilot to just fly the plane.

Yule said he hoped applying the technology to hill country farms would help arrest the country's falling stock rate over the last 30 years -- in part caused by farmers not using enough fertiliser.

Yule said there was 8 million hectares of hill country in New Zealand and 55 per cent of it was farmed. There were around 12,000 hill country farms with an average size of 676 hectares.

Farmers typically spent around $75,000 a year on fertiliser -- about $110 to $120 per ha.

But analysis showed it should be more like $140 per ha, Yule said.

If there is a blanket increase in the amount of fertiliser spread on a farm, then it would cost a lot more. The technology would allow some areas to have more fertiliser and others to have less, boosting potential productivity by 25 per cent.

Yule said once the initial research on the eight farms was complete they would move onto focus farms.

"The whole project is still a number of years away from being completed. This is really the first stage. People are excited about what the technology can offer."

He is hopeful the project will be able to go out to other farms by next year.

Yule said the spectral imaging tool would cost around $15 per hectare -- about 10 per cent of what farmers typically spent on fertiliser.